The present invention relates to a control system for a hydraulically-operated transmission of a vehicle, and particularly to a control system for a hydraulically-operated transmission of a vehicle which performs hydraulic control of a working oil according to a temperature of the (the xe2x80x9cworking oil temperaturexe2x80x9d) working oil of the hydraulically-operated transmission.
A hydraulically-operated transmission changes the shift positions and controls an engagement force of a lockup clutch by adjusting a hydraulic pressure of the working oil. In this control operation, the viscosity of the working oil changes depending on the working oil temperature. Therefore, the change of working oil viscosity affect the control operation of the transmission correspondingly. A technique for coping with such an inconvenience is disclosed in Japanese Patent Laid-open No. Sho 62-63248, wherein the working oil temperature of a hydraulically-operated transmission is detected by an oil temperature sensor and the hydraulic control of the working oil is performed according to the detected working oil temperature.
In stead of detecting the working oil temperature by the oil temperature sensor, a technique of estimating the working oil temperature based on a cooling water temperature of an internal combustion engine connected to the input side of the transmission together with an operating condition of the transmission is disclosed in Japanese Patent Laid-open No. Hei 8-233080.
The above technique of detecting a working oil temperature by the oil temperature sensor, however, has a problem. The oil temperature sensor of the above technique can not accurately detect the working oil temperature suitable for hydraulic control over an entire temperature range given the location of the oil temperature sensor mounted on the vehicle during the mass production process of the vehicle. Therefore, the detected temperature changes depending on the performance of the sensor, the mounted location, and the mounting manner of the sensor.
The method of estimating the working oil temperature disclosed in Japanese Patent Laid-open No. Hei 8-233080 has a problem whereby the difference between the estimated working oil temperature and the actual working oil temperature tends to be large, particularly, when the working oil temperature is high.
An object of the present invention is to provide a control system for a hydraulically-operated transmission of a vehicle which is capable of accurately obtaining a working oil temperature suitable for hydraulic control for any temperature range.
To achieve the above object, the present invention provides a control system for a hydraulically-operated transmission of a vehicle. The transmission is connected to a crankshaft of an internal combustion engine and has a plurality of friction engagement elements. The control system changes a shift position by switching the engagement states of the friction engagement elements and comprises a working oil temperature detecting means, a cooling water temperature detecting means, a transmission operating condition detecting means, a working oil temperature estimating means, a weighting factor calculating means, an actual working oil temperature calculating means, and a hydraulic pressure control means. The working oil temperature detecting means detects a working oil temperature of the transmission. The cooling water temperature detecting means detects a cooling water temperature of the engine. The transmission operating condition detecting means detects an operating condition of the transmission. The working oil temperature estimating means calculates an estimated value of the working oil temperature on the basis of the detected cooling water temperature and the detected operating condition of the transmission. The weighting factor calculating means calculates a weighting factor according to the working oil temperature detected by the working oil temperature detecting means or the estimated working oil temperature calculated by the working oil temperature estimating means. The actual working oil temperature calculating means calculates a weighted average value of the working oil temperature detected by the working oil temperature detecting means and the estimated working oil temperature calculated by the working oil temperature estimating means by using the weighting factor calculated by the weighting factor calculating means, and outputs the calculated weighted average value as an actual working oil temperature. The hydraulic pressure control means controls a hydraulic pressure of the working oil according to the actual working oil temperature outputted from the actual working oil temperature calculating means.
With this configuration, the estimated working oil temperature is calculated on the basis of the detected cooling water temperature during the start of the engine and the detected operating condition of the transmission. Further, the weighted average value of the detected working oil temperature and the estimated working oil temperature is calculated by using the weighting factor which is calculated according to the detected working oil temperature or the estimated working oil temperature. Furthermore, the weighted average value is outputted as the actual working oil temperature. The hydraulic pressure of the working oil is controlled according to the actual working oil temperature. Accordingly, by suitably setting the weighting factor, it is possible to obtain an accurate actual working oil temperature over the available entire temperature range on the basis of the estimated working oil temperature and the detected working oil temperature. Therefore, by suitably setting the weighting factor, the control system of the present invention can perform an optimum hydraulic control at all times corresponding to a change in the working oil temperature.
Preferably, the weighting factor calculating means sets the weighting factor so that the weight of the detected working oil temperature becomes larger as the detected working oil temperature or the estimated working oil temperature becomes higher.
With this configuration, the weighting factor used for calculating the weighted average value is set so that the weight of the detected working oil temperature becomes larger as the detected working oil temperature or the estimated working oil temperature becomes higher. Accordingly, it is possible to obtain an actual working oil temperature suitable wherein the accuracy of the estimated working oil is high in a low temperature range of the working oil temperature and the accuracy of the detected working oil temperature is high in a high temperature range of the working oil temperature.
Preferably, the actual working oil temperature calculating means outputs the detected working oil temperature as the actual working oil temperature, when the cooling water temperature detecting means fails.
Preferably, the transmission operating condition detecting means includes a plurality of sensors for detecting the operating condition of the transmission, and the actual working oil temperature calculating means outputs the detected working oil temperature as the actual working oil temperature, when at least one of the plurality of sensors fails.
The vehicle has a radiator for lowering the cooling water temperature, and the transmission has a torque converter, a plurality of gears, and a working oil passage for circulating the working oil into the radiator. Therefore, the working oil temperature estimating means calculates the estimated working oil temperature on the basis of a first temperature rise amount per unit time due to the operation of the torque converter, a second temperature rise amount per unit time due to the plurality of friction engagement elements, a third temperature rise amount per unit time due to the stirring of the working oil by the plurality of gears, a temperature change amount per unit time due to circulation of the working oil through the radiator, and a temperature drop amount per unit time due to heat radiation to the atmosphere.